Home' Accord : Accord December 2015 Contents Feature 9
Oticon Frequency Lowering
Access to high-frequency speech sounds
with Speech Rescue technology
Frequency lowering is a well-known technology in hearing aids that shifts high-frequency sound to lower
spectral regions. Research and clinical findings have revealed the challenges of developing a strategy that
can provide access to high-frequency speech without introducing unacceptable amounts of low-frequency
Oticon Speech Rescue, the latest frequency lowering processor on the market, is explicitly designed to
transmit temporal features of high-frequency speech with minimal distortion of low-frequency spectral
features. It is unique because it uses a multi-layered lowering technique that overlaps copied segments from
a wide region in the high-frequency input in order to present the information in a narrow region in the low
frequencies. Prescription of Speech Rescue is based on the principle of Maximum Audible Output Frequency
(MAOF), which means that the lowered input will be at the border of the patient’s usable hearing.
Here, we highlight the principles behind the Speech Rescue strategy and configurations, and describe the
importance of providing a correct frequency lowering setting to optimise the benefit for the patient with a
severe-to-profound hearing loss.
EDITORS OF THIS ISSUE
Kamilla Angelo1, Joshua M. Alexander2, Thomas U. Christiansen1, Christian S. Simonsen1
& Claus F.C . Jespersgaard1.
1 Oticon A/S, Headquarters, Denmark
2 Dept. of Speech, Language, & Hearing Sciences, Purdue University
Thank you to Ryan McCreery for providing helpful insights and work with evaluating the Speech Rescue algorithm and settings. Thank
you to Anne Specht Petersen and Maria Brorsson for running all clinical testing at the Oticon Headquarters, Denmark.
If you have any questions to the content of the white paper please contact Kamilla Angelo, firstname.lastname@example.org.
Oticon - World Leaders in BrainHearingTM Technologies
For more information, please contact your Oticon representative
on Freecall 1800 633 738 or visit www.oticon.com.au
The brain constantly uses both ears to orient
itself and know what’s happening
in the environment
The brain depends
on its ability to
recognise a sound
in order to make
sense of it
The brain has to know
where to focus in noisy
The conventional industry
mindset is to compensate
for damage in the ear.
We call this ear hearing.
By thinking brain first,
we aim to help the brain
make sense of the sound
it receives from the ears.
Maintain as much of the surrounding
environment as possible
Prioritise speech information over other sounds
Keep the natural sound level
differences occurring at each ear
Preserve the important details of sounds
Let both ears work together constantly
Optimise all technologies so that they perform
according to the individual’s own unique needs
Match an individual’s own experience of sound
Deliver varying degrees of directionality, only resorting to
full directionality when absolutely necessary
In the MarkeTrak VIII study carried
out in 2010, Kochkin, S. et al
measured average hearing
instrument user satisfaction at 79%
In the Oticon Satisfaction Study, 2013,
average hearing instrument user
satisfaction with instruments with
BrainHearingTM technology was 96%.
That’s a staggering 17% increase!
Eriksholm Research Centre,
which is part of Oticon, has been
researching and implementing
BrainHearingTM technologies for over
READ THE SURVEY AT
Frequency lowering technology
Frequency lowering is the umbrella term for the signal
processing in hearing aids that makes high-frequency
sounds available at lower frequencies, where the patient
has usable hearing. Today, frequency lowering is achieved
in as many different ways as there are hearing aid manu-
facturers. However, conceptually, the different technolo-
gies use one of three basic techniques: compression,
transposition, and composition (Fig. 1). With frequency
compression (e.g. SoundRecover by Phonak) high frequen-
cies are brought to lower frequencies by squeezing fre-
quency content together in a smaller space. This is done
for sounds above a selected start frequency, and distortion
is thus introduced as the frequency spacing in a band is
reduced to fit within the audible bandwidth of the patient.
Depending on the position of the start frequency, the
low-frequency spectra important for vowel identification
are likely to be altered, at the risk of creating vowel confu-
sion. Frequency transposition (e.g. Audibility Extender by
Widex) captures a portion of the high-frequency spectrum
and reproduces it at a lower spectral position, where it is
mixed with the original signal. To avoid compressing the
high frequencies only a small section is selected (Kuk et
al., 2006; Kuk et al., 2009). Frequency composition is the
latest technology on the market. It superimposes a high-
frequency source band onto a low-frequency destination
band, but it first divides the source band into 2 or 3 seg-
ments and then overlaps them in the destination band in
order to present information from a wider input region in
a narrower output region. For a comprehensive and recent
review of the various strategies see Alexander (2013) or
listen to the audiology online course #23437 “Individual
variability in recognition of frequency-lowered speech”
by the same author: http://www.audiologyonline.
Fig. 1 Frequency Lowering Strategies
Figure 1: Frequency lowering strategies.
From top to bottom: Frequency Composition, Compression and Transposition.
With Frequency Compression, sounds above a selected start frequency are
squeezed to fit within the audible bandwidth of the patient. Depending on the
position of the start frequency, the low-frequency spectra important for vowel
identification are likely to be altered, at the risk of creating vowel confusion.
Frequency Transposition cuts out a portion of the high-frequency spectrum
and reproduces it at a lower spectral position. To avoid compressing the high
frequencies only a small high-frequency section is selected. Frequency
Composition superimposes a high-frequency source band on a low-frequency
destination band, but it first divides the source band into 2 or 3 segments and
then overlaps them in the destination band in order to present information from
a wider input region in a narrower output region. Note that with frequency com-
position the output bandwidth is intact. Whereas for frequency compression
and for some variations of transposition there is an output band-limiting effect.
Frequency lowering technologies
Frequency lowering is the umbrella term for the signal processing in hearing aids that makes high-
frequency sounds available at lower frequencies, where the patient can hear. Today, frequency lowering
is achieved in as many different ways as there are hearing aid manufacturers. However, conceptually, the
different technologies use one of three basic techniques: compression, transposition, and composition
(Fig. 1). Frequency composition is the latest technique on the market. It superimposes a high-frequency
source band onto a low-frequency destination band, but it first divides the source band into 2 or 3
segments and then overlaps them in the destination band in order to present information from a wider
input region in a narrower output region.
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